The present invention relates to a bone tissue implant and a fabricating method of the implant. The implant of the present invention can be used as artificial joints, bones, or tooth roots, for surgical treatment of humans, pets, domestic animals, and the like. Specifically, it can be used as a replacement for bone tissues in a living body.
It is well known that an artificial joint is composed of a stem portion, a head portion, and an acetabular portion. The stem and head portions of the conventional artificial joint are composed of bioinert materials, e.g., titanium alloy, or alumina ceramics. These materials retain greater strength and resist corrosion. The acetabular portion of the conventional artificial joint is composed of high-density polyethylene, which offers adequate resiliency and biotolerance. When the above artificial joint is implanted as a replacement of a damaged hip joint, the stem portion is implanted in a hollow part perforated for the upper part of a femur through bone cement made of polymethyl methacrylate (PMMA), and the acetabular portion is implanted in a coxal bone located in the lower part of a pelvis through the bone cement. The implanted artificial joint sufficiently functions as a hip joint, retaining greater strength and avoiding corrosion.
However, it is well known that the PMMA bone cement generates very high heat of polymerization when methyl methacrylate monomer is polymerized to harden. Therefore, the problem exists that the heat of polymerization seriously damages bone tissues where the bone tissues and bone cement contact. To solve the above problems, a following therapy has been performed, which uses natural healing power of a patient. In the therapy, the operation in which the stem portion and the acetabular portion of the artificial joint were implanted was performed so that these portions directly contact the bone tissues without using bone cement. Subsequently, the patient was made to keep quiet in bed until the artificial joint was sufficiently fixed to the bone tissues.
When the above therapy was performed, the mesenchymal stem cells which exist in patient bone marrow migrate to the clearance between the artificial joint and the bone tissues and then are adhered. Subsequently, the adhered mesenchymal stem cells proliferate and differentiate to osteoblasts having high bone repair activity. Then, the osteoblasts produce bone matrix. The bone matrix covers the surfaces of the artificial joint and bone tissues to fill the clearance. As a result, the artificial joint is fixed.
Japanese Laid-Open Patent Publication No. 3-45267 discloses filling materials for a bone defective part and a bone vacant part. The filling materials are composed of body fluid containing osteoblasts and/or osteoprogenitor cells, which is obtained from an animal, and calcium phosphate compounds. The filling materials for the bone defective part and the bone vacant part are prepared by the steps of adsorbing the body fluid from the animal itself to be treated to porous or granular calcium phosphate compounds, and culturing artificially, if necessary. The bone defective part and the bone vacant part of the animal are filled with the resultant filling materials for the bone defective part and the bone vacant part. The filling materials have excellent biocompatibility, and do not cause xenobiotic reaction and inflammatory reaction. In addition, the leakage of the filling materials from a filling site is very little. Therefore, rapid formation of new bone may be expected.
On the other hand, the conventional artificial joint has possibility for damaging the living tissues, such as circumferential bone tissues, since PMMA bone cement for connecting the artificial joint to the bone tissues generates a heat during the polymerization, and also the residual monomer elutes out. Therefore, when the artificial joint is used under a mechanically (i.e., physically) severe condition, the boundary face between the stem or acetabular portion and bone tissues surrounding it is destroyed. In addition, there is remarkably high possibility that the artificial joint will become loose or disengaged.
Further, the above-mentioned conventional therapy using natural healing power requires a long period of time until the mesenchymal stem cells to the surfaces of the artificial joint and bone tissues, and then produce bone matrix. In particular, an aged living body requires a very long period of time for being completely recovered, since they have less mesenchymal stem cells in their body and bone tissue repair speed by osteoblasts and osteoprogenitor cells is remarkably slow.
In the conventional filling materials for the bone defective part and the bone vacant part, porous or granular calcium phosphate ceramics are used as a substrate. The ceramics composed of these substrates have low mechanical strength, and are typically brittle. Therefore, they could not be used for the site in which a large load is applied or elastic deformation is required.